The present invention relates to a device for suitably controlling the idling speed of an internal combustion engine.
Various devices for controlling the idling speed of an internal combustion engine have been known. Among these devices, a device for controlling the idling speed by controlling the amount of air fed into the cylinder of the engine has been put into practical use. This device comprises a bypass passage bypassing a throttle valve and a vacuum-operated flow rate control valve arranged in the bypass passage, and the opening area of the flow rate control valve is controlled by an electromagnetic means which controls the level of the vacuum acting on the vacuum chamber of the flow rate control valve. In addition, another device for controlling the idling speed was recently proposed in which the flow area of the control valve arranged in the bypass passage is controlled by a step motor. However, since such a device is so constructed that the data indicating the step position of the step motor, is stored in a single memory, if errors occur in the content of the memory, a problem occurs in that it is difficult to control the idling speed. In order to eliminate such a problem, a feedback control-type device for controlling the idling speed has been proposed in which a sensor is provided for detecting the step position of the step motor. However, such a feedback control-type device has such drawbacks that the manufacturing cost is increased and the durability and the reliability deteriorate.